Prevent repeat restaurant orders on custom php order page

Prevent repeat restaurant orders on custom php order page On custom live online ordering menu page, if someone hits Process order button more than once before the page has a chance to order, duplicate orders are created. Either make it so there can only be one order per session, or have the page prevent the Process button being hit again, or something. Whatever works best. I don't think the page has any session on it at all. I can't give ftp access. I can send files and load them myself, but since this is an active site, and I've had issues with programmers testing and messing things up by accident, I want to load and test all files myself so I can quickly reload a backup if what you give me causes any other issues. Need in one day.